This invention relates to fluid collection devices and more particularly to fluid collection devices such as blood collection devices having blood phase partitioning means.
In taking blood samples for clinical testing, for example, it is common practice to employ an air evacuated blood collection tube and a needle holder having a double-ended needle cannula for drawing the blood sample. After the distal end of the needle is inserted into a body vessel, such as a vein, the tube stopper is pierced by the proximal end of the needle so that whole blood is drawn into the tube by the negative pressure. Where it is desired to analyze the serum or the plasma component of the blood, the tube is placed in a centrifuge where the lighter phase, serum or plasma, is centrifugally separated from the heavier phase which includes the blood cells. As is well known, when serum is to be separated, the whole blood is allowed to clot so that upon centrifugal separation, the lighter phase is serum. When plasma is to be tested, an anticoagulant is used with the blood to prevent clotting so that the centrifugally separated lighter phase is plasma.
Various devices have been used to isolate the separated phases from each other. For example, the collection tube may be carefully opened after separation and the lighter phase removed such as by carefully siphoning it, or a separating device may be inserted through the light phase and positioned at the interface or between the phases so that the lighter phase only can be poured from the tube. These methods and devices have the disadvantages of being relatively complicated in operation, time consuming, and they present the possibility that the specimen will be contaminated or that personnel will be exposed to a disease-carrying specimen.
In U.S. Pat. No. 3,780,935, a collection tube is opened before centrifugation and a dispenser containing a sealant of silicone fluid and silica is inserted in the open end of the blood filled tube. The sealant has a specific gravity intermediate the specific gravity values of the two phases and is released from the device by centrifugal forces during centrifugation. The sealant moves to a position between the two phases to provide a partition or barrier between the phases. This method has the undesirable feature that the collection tube must be opened by personnel in order to insert the dispenser. Also, silicone fluid based sealants have produced oil-like films or "droplets" in the lighter phase causing the clogging or tubing, especially when using automated chemistry or blood analyzers.
U.S. Pat. No. 3,852,194 discloses the use of a gel-like material such as silicone fluid and a filler which is disposed in the collection tube before the collection tube is used to draw blood from the patient. This material has a specific gravity intermediate the specific gravities of the separated phases so that it forms a barrier between the separated phases. This patent also gives examples of various oils that may be used. While this reference discloses an arrangement whereby the phases are isolated without opening the collection tube, there is generally the problem of oil from the silicone gel-like material causing clogging of tubing in the testing equipment, as mentioned above.
In U.S. Pat. No. 3,909,419, a plurality of micro encapsulated beads of gelatin are disposed between a pair of cylinders with these elements having specific gravities related such that, after the phases have been separated, the speed of the centrifuge can be increased to cause the cylinders to move toward each other to rupture the beads so that the gelatin forms a seal between the two phases. This device requires the relatively expensive manufacture of encapsulated beads, and necessitates centrifugation at two different speeds.
Various other types of centrifugally actuated phase separators have been proposed. Some include relatively complicated valves, filters or pistons, and some require relatively expensive collection tubes having a removable closure at each end in order to enable the device to be operable for both serum and plasma.